How to Get More Power from Your L92 Engine (Bolt-Ons)

For many people, upgrading an L92 starts with adding a cold air intake and aftermarket exhaust. This will definitely free up a few horsepower and people will be pretty surprised to look over and see a full-size SUV making that sort of noise.

Trucks often come with mechanical fans that sap horsepower. An electric fan kit will free up that power.

These mods can be done in your garage, but the tune won’t be optimized.

We recommend that you talk to your local chassis dyno tuner and decide on a computer programmer.

Whether you’re towing on low-octane or springing for good fuel, a tuner can dial the ECM and take it to the next level. Raising the factory redline is a big part of this because it allows your vehicle to be in the meat of the powerband longer.

Torque limiting can be completely shut off, shift points can be raised and it makes it easier to tune for a bigger cam and injectors later on. Before beginning the tuning process, we recommend installing a colder thermostat to open up the L92 tuning window.

Below are some more upgrades you can make to improve the performance of an L92 engine.

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Upgrading the L92 Camshaft and Valvetrain

Properly done, it makes more power and torque than a much bigger engine-yet idles well and retains most of the gas mileage. If you don’t want to mess with it, you can easily convert to a standard non-VVT one- or three-bolt cam.

To maximize torque in the mid-range in a truck cam, aftermarket manufactures close the intake valve at about 35-40 degrees (@.050 in.) after bottom dead center and alter the intake valve opening point to set the idle quality.

The 6.2L engine can take a little more cam than a 5.3 or 6.0L engines and still idle well.

What if you already have a power adder?

Generally, supercharger cams and nitrous cams will have slightly more lobe separation and longer exhaust duration. Turbo cams reduce overlap with less exhaust duration split in relation to the intake.

Intake Duration (@ 0.050 in.)

Horsepower at the wheels after bolt-ons

Idle Quality

Notes

198° (Stock)

325-340 whp

Smooth

Heavy drivetrain.

215°

+50 hp

Slightly noticeable

Good with auto and stock converter.

220° - 230°

+75 hp

Steady lope

Converter recommended. Still can drive daily.

230° - 240°

+100 hp

Lopey

Fly-cutting the pistons may be required. Heads and intake good for another 40+ hp.

Drop-in .500-in. lift cams are popular, but LS6 springs allow you to run .550-in. lift and extend the rpm range. Spring life isn’t a problem because trucks generally don’t spend a lot of time at high rpm. After all, a C5 Z06’s LS6 had .555-in. lift and will happily go 150,000+ miles with normal use. Beyond that, .575 to .600 in. isn’t a problem with dual valve springs.

The stock rockers are good up to 175 lbs. of seat pressure and 450 lbs. open. You will want to install a trunnion kit for added reliability. When you’re pulling the cam, switch out the spring-loaded timing chain tensioner for the more-reliable wedge-style (early) LS2 damper.

L92 Power Adders

L92’s are a popular choice for people that want to stay naturally aspirated, but if you do decide to boost, here are a couple of things to address:

A 4-corner steam kit reduces hot spots that can cause the rings to butt and snap the piston’s ring lands.

Any power adders will put you well past the limitations of the fuel injectors. We’ve addressed those in the next section below on fuel system upgrades.

Okay, here’s the fun stuff:

A nitrous oxide kit(at low settings) is great for street driving with stock internals. Up to a 200-shot is common. Keep in mind the tight piston ring gap is the limiting factor beyond that. If you’re wanting to get serious, a single-plane intake is less prone to break from a nitrous backfire. A plate system has better distribution than the original intake, but an eight-nozzle fogger system is even better. Running higher octane fuel is advised.

Truck engine bays make fitting turbos easy. Single turbo systems using turbo exhaust manifolds are an inexpensive way to make big power. If you’re running a single turbo, the T4 hot-side fits well, but the small turbine diameters limit exhaust flow. The 650 whp begins to feel like 400 did in a hurry, so take this into consideration. V-band style exhaust housings are available with larger turbines and make plumbing easier. Although twins are a little more expensive out of the box, you’ll have more room to grow.

A Roots-style supercharger is dependable and makes great torque in the low- and mid-rpm range. It’s great for melting tires. An original 6.2L is a rarity and owners usually turn them into hot rods and keep them for a long time. That being the case, a burly blower is a good investment.

A centrifugal-style supercharger is lightweight and makes more power at high rpm. This is partially due to a larger intercooler mounted in front of the radiator. They don’t have quite the curb appeal of a Roots, and aren’t as common.

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Upgrading the L92 Fuel System and Tuning

We recommend looking at the injector’s part number before taking it to the tuner. The L92 came with 30-lb. injectors supporting roughly 390 whp. Several other injectors are available with the same connector and length between o-ring centers.

Many fuel system upgrade options are available including using the flex-fuel pumps which are good for another 100+ whp, but the modules (baskets) are different and it may be easier just to swap the entire tank. The factory pump is good to about 430 whp.

When running boost, you can use a water-methanol system to supply extra fuel and lower charge air temps.

One last note on tuning: The L92 has a 58x reluctor ring and isn’t compatible with the early LS ECMs. It’s best to keep the E38 ECM as it’s faster and tunes better with bigger cams.

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Upgrading the L92 Intake Manifold and Throttle Body

The intake is good and has a 4-bolt 87mm throttle body. The big plenum and long runners made better low-end torque and makes good power from idle through 6,000 rpm. It’s also very good for boost, but not good for engines built for big nitrous.

If you have the L92 in a vehicle with deep gears, big converter, cam, and the rev limit bumped, you may want to trade a little of that low-end torque for some top-end horsepower. If so, go with a long-runner cast tunnel ram. Gains of 35 whp are possible with the crossover point starting at around 5,000 rpm.

Want it all?

Go with the Edelbrock cross-ram. The low-end torque of the factory and the top-end of the tunnel ram. Dual throttle bodies to top it off.

In most cases a single plane is the wrong way to go, but might make sense if you’re running a lot of nitrous because it’s stronger and the cylinder-to-cylinder mixture distribution can be better.

Ask your tuner about going with a speed density tune. Doing so will remove the MAF restriction and will give you a bit more power.

[Trying to find an LS or LS-based Vortec engine for a swap or build? Check out Part 1 and Part 2 of our LS Spotter’s Guide.]

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Upgrading L92 Cylinder Heads

(Image/YouTube)

The L92 cylinder heads are similar to the LS3 heads except they used a heavier solid stem intake valve.

The stock heads can be CNC-ported for more airflow. Flow numbers can be as high as 373 cfm at .700 lift. Lightweight hollow stem LS3 valves will drop right in. Between the light valves and better springs, the engines will pull cleanly to 7,000 rpm. Keep in mind, if you’re looking to boost to 800+ hp; a heavy duty aftermarket stainless intake valve is a bit tougher and won’t tulip as quickly from the heat. Milling the heads .030 will bump compression to 10.8:1 and will increase power everywhere. Keep in mind, piston to valve clearance will be tight with cams beyond 230 at .050 in. of intake duration.

A better option is aftermarket heads. They reduce down time, they’re all-new, and you can usually offset the added cost by selling your original heads. Valve angles are typically laid over to 13.5 degrees for increased piston to valve clearance. They flow better and the cross-sections are great for naturally aspirated or boosted engines. When comparing heads, look at the .400 in. lift numbers as a general indicator of how the heads will perform. With a medium-sized cam, 475+ whp naturally aspirated is common even with the heavier truck drivetrain.

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Upgrading the L92 Rotating Assembly

On the L92 engine, the pistons are the weak link and you probably already know someone who has popped one.

They have stronger wristpins, thicker ring lands, and the added valve reliefs allow you to run big cams. If you’re going over 800 hp, a set of .200 wall tool-steel pins is a good idea.

The L92’s Gen. 4 rods are stronger than the Gen. 3 rods and have full floating pins. They can handle about 800 hp and 7,000 rpm in boosted applications (at least for a while). They are likely to bend before they break when subjected to real track conditions.

If you’re getting forged pistons, upgrade to forged connecting rods at the same time. Big 7/16-inch rod bolts will go a long way to keep things together over 7,000 rpm.

The L92 crank was cast but strong. The main reason for a stroker crank is added cubic inches. With heads and manifolds available that breathe well above 7000 rpm, more cubes can bring the power peak back into hydraulic roller territory for more power under the curve.

The 6.2L aluminum blocks had slightly longer cylinder sleeves than the iron blocks 5.500 in. vs. 5.430 on average). Much of the piston skirt drops out of the bottom of the cylinder at BDC. The best piston manufacturers have compensated for this by eliminating skirt taper until a point well above where it meets the bottom of the cylinder sleeve at BDC. Any skirt taper at this intersection acts as a razor blade and will wear out the piston quickly. This is especially true of the 427ci combination and the piston design is critical to long life.

The blueprint deck height of the block is 9.240 in. It’s best to measure deck height before ordering your rotating assembly. Thicker head gaskets or using an aftermarket 6.098-6.100 in. rod will ensure enough piston-to-head clearance.

Engine Size

Bore Dia.

Piston Comp. Height

Stroke

Rod Length / Wristpin

6.2L (376 c.i.d. - stock)

4.000 in.

1.338 in.

3.622 in.

6.098 in. / 0.9431-0.9449 in.

6.8L (416 c.i.d.)

4.070 in.

1.110 in.

4.000 in.

6.125 in. / 0.927 in.

7.0L (427 c.i.d.)

4.070 in.

1.050 in.

4.100 in.

6.125 in. / 0.927 in.

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Upgrading the L92 Engine Block

(Image/LS1Tech)

The L92 engine block has a 4.065-in. bore diameter and can be safely bored to 4.080 in.

However, it’s better to hone up in .005 increments to maximize strength.

You can make 850 whp with a couple of simple upgrades like head studs and LS9 head gaskets. Race gas, E-85, or water-methanol injection is required.

It’s always worth it to invest in a chassis dyno tune to find fuel, spark, and other issues that are harder to spot at the track.

The factory main caps aren’t doweled. It’s better to reduce ignition timing and compensate with added boost to reduce the cylinder pressure spikes that can lift heads and cause the main caps to dance.

Author: Brian Nutter
After a stint in the U.S. Air Force, Brian Nutter studied at the Houston, TX-based School of Automotive Machinists in 1997. The early part of his automotive career included working for engine builders Scott Shafiroff and C.J. Batten, followed by several years developing performance pistons at Wiseco Piston Co. Today, Brian develops performance parts for Summit Racing Equipment and is a regular OnAllCylinders contributor. For fun, he runs his 427-powered C5 Z06 in ECTA land-speed racing, at OPTIMA® street car events, and at a mix of autocross, drag racing, and track days.